1. Field of the Invention
The present invention relates to a measuring method in which a circuit or a circuit element of a semiconductor device is operated and an output from the circuit or the circuit element is read, and to a method of inspecting by using the measuring method to inspect whether a pixel portion operates normally. More particularly, the present invention relates to a non-contact type inspection method and a non-contact type inspection device using the non-contact type inspection method. The present invention also relates to a method of manufacturing a semiconductor device, which includes an inspection step using the inspection method, and to a semiconductor device manufactured by using the manufacturing method. Further, the present invention relates to a method of manufacturing an element substrate including an inspection step using the inspection method, and to an element substrate manufactured by using the manufacturing method.
2. Description of the Related Art
In recent years, attention have been paid on techniques for forming a thin-film transistor (TFT) by using a semiconductor film (having a thickness of about several nanometers to several hundred nanometers) formed on a substrate having an insulating surface. This is because the demand for active matrix semiconductor display devices included in the category of semiconductor devices has been increased. Typical examples of the active matrix semiconductor display devices include liquid crystal displays, organic light emitting diode (OLED) displays, and digital micromirror devices (DMDs).
A high degree of mobility can be achieved in TFTs in which a semiconductor film of a crystalline structure is used as an active layer (crystalline TFTs). Therefore, it is possible to realize an active matrix semiconductor display device capable of high-resolution image display by forming TFTs of such a kind with functional circuits integrated on one substrate.
An active matrix semiconductor display device is completed by performing various manufacturing processes. For example, essential processes for manufacturing an active matrix liquid crystal display are a pattern forming process for performing forming and pattern forming of a semiconductor film, a color filter forming process for realizing a color display, a cell assembly process for forming a liquid crystal panel by enclosing a liquid crystal between an element substrate having devices including a semiconductor and a counter substrate having a counter electrode, and a module assembly process for completing the liquid crystal display by attaching drive components for operating the liquid crystal panel and a backlight to the liquid crystal panel assembled in the cell assembly process.
Ordinarily, each of the above-described processes includes an inspection step though the requirements for inspection steps therein vary more or less, depending on the kind of the liquid crystal display. If a defective can be picked out in an earlier stage of the manufacturing process before it is finished as a product, execution of the subsequent processes with respect to the defective panel can be avoided. Therefore the inspection step is highly effective in reducing the manufacturing cost.
The pattern forming process includes as one of its inspection steps a defect inspection after pattern forming.
The defect inspection after pattern forming is an inspection for detecting, after pattern forming, a portion where a malfunction occurs due to variation in width of semiconductor film, insulating film and wiring pattern (hereafter, simply referred to as a pattern), or a portion where a wiring is broken or short-circuited by dust or by film forming failure, or for ascertaining whether circuit or circuit element to be inspected operates normally.
Methods for such defect inspection are generally grouped into an optical inspection method and a probe inspection method.
An optical inspection method is a method of identifying a faulty portion (defect) by reading with a CCD or the like a pattern formed on a substrate and by comparing the read pattern with a reference pattern. A probe inspection method is a method of determining whether a portion is defective or non-defective by setting fine pins (probes) on terminals on the substrate side and by measuring a current or voltage between the probes. Generally, the former is called a non-contact type inspection method and the latter is called a contact stylus type inspection method.
Although it is possible to determine whether an element substrate is defective or non-defective by using either of these inspection methods, each inspection method has both advantages and disadvantages.
The optical inspection method have a problem in that if the inspection is performed after the completion of formation of a plurality of layered patterns, it is difficult to identify each pattern in lower layers, and it is, therefore, difficult to determine whether a circuit or a circuit element is defective or non-defective by performing detection of a defective portion. To avoid this problem, the inspection may be performed each time a pattern is formed. In such a case, however, the inspection step is complicated and the time required to perform the whole manufacturing process is increased. The probe inspection methods have a problem in that when probes are set directly on wiring or probe terminals, there is a fear of the wiring or probe terminals being scratched to produce minute dust. Dust produced during the inspection step becomes a cause of an undesirable result, i.e., a reduction in yield in subsequent processes.